1. Field of the Invention
The present invention relates to a reference voltage generator for generating a reference voltage within a semiconductor integrated circuit.
2. Description of the Related Art
In recent years, the improvement of the precision of an electronic apparatus has progressed, and the increased precision of an IC for controlling the electronic apparatus has been required. As a result, in the IC, especially, a power management IC represented by a voltage detector or a voltage regulator, along with the miniaturization and the versatility of a portable apparatus to be loaded with the IC, it is required that even when a temperature is changed in the inside of the IC due to a change in ambient temperature environment, a reference voltage generator can generate a reference voltage with high precision, that is, temperature characteristics of the reference voltage become flatter.
A circuit used in a reference voltage generator in the related art is described with reference to FIG. 4. FIG. 4 is a circuit diagram of the reference voltage generator in the related art as shown in Japanese Published Patent Application JP 56-108258. A depletion NMOS transistor (hereinafter referred to as a D type NMOS transistor) 1 which is connected so as to function as a current source causes a constant current to flow into a diode-connected enhancement NMOS transistor (hereinafter referred to as an E type NMOS transistor) 2. By causing this constant current to flow into the E type NMOS transistor 2, a reference voltage corresponding to threshold voltages and sizes of the respective transistors is generated in the E type NMOS transistor 2.